Reef Strontium is intended to restore and maintain strontium to levels found in natural seawater without affecting pH. Strontium is utilized in the same manner as calcium and holds a similar importance in maintaining a vigorous level of growth. Strontium occurs in natural seawater at a concentration of about 8 to 10 mg/L. It is chemically very similar to calcium, and many organisms incorporate it in their skeletons along with calcium. Its addition to reef aquariums aids the growth of corals, coralline algae and other organisms that lay down a calcereous skeleton or shell, including tridacnid clams. 500ml.